Adjustable meander line resistor

ABSTRACT

An adjustable meander line resistor comprises a plurality of series circuits. Each series circuit comprises a first resistor formed on a first doped region of a transistor, a second resistor formed on a second doped region of the transistor and a connector coupled between the first resistor and the second resistor. A control circuit is employed to control the on and off of the transistor so as to achieve the adjustable meander line resistor.

BACKGROUND

The semiconductor industry has experienced rapid growth due toimprovements in the integration density of a variety of electroniccomponents (e.g., transistors, diodes, resistors, capacitors, etc.). Forthe most part, this improvement in integration density has come fromshrinking the semiconductor process node (e.g., shrink the process nodetowards the sub-20 nm node). As the demand for miniaturization, higherspeed and greater bandwidth, as well as lower power consumption andlatency has grown recently, there has grown a need for smaller and morecreative packaging techniques of semiconductor dies.

Modern electronic devices such as a notebook computer comprise a varietyof memories to store information. Memory circuits include two majorcategories. One is volatile memories; the other is non-volatilememories. Volatile memories include random access memory (RAM), whichcan be further divided into two sub-categories, static random accessmemory (SRAM) and dynamic random access memory (DRAM). Both SRAM andDRAM are volatile because they will lose the information they store whenthey are not powered. On the other hand, non-volatile memories can keepdata stored on them permanently unless an electrical charge is appliedto non-volatile memories. Non-volatile memories include a variety ofsub-categories, such as electrically erasable programmable read-onlymemory (EEPROM) and flash memory.

A DRAM circuit may comprise a plurality of DRAM memory cells arranged inrows and columns. A DRAM cell is made up of a single metal oxidesemiconductor (MOS) transistor and a storage capacitor connected inseries. The MOS transistor functions as a switch coupled between a bitline and an electrode of the storage capacitor. The other electrode ofthe storage capacitor is connected to the corresponding electrodes ofthe other cells on the same column and is biased to a plate voltage. Thestorage capacitor contains one bit of information. By enabling a wordline coupled to the gate of the MOS transistor, data stored in thestorage capacitor can be written in or read out. In particular, during awrite operation, the data to be written is placed on the bit line. Byturning on the MOS transistor, the storage capacitor will be eithercharged or discharged depending on the data bit and the original logicstate of the storage capacitor. On the other hand, during a readoperation, the bit line is pre-charged to a voltage. By turning on theMOS transistor, the voltage change on the bit line indicates the logicstate of the storage capacitor.

As semiconductor technologies evolve, embedded DRAM (EDRAM) basedsemiconductor devices have emerged as an effective solution to furtherreduce the physical size of a semiconductor chip and improve theperformance of memory circuits and logic circuits as a whole. EDRAM isfabricated on the same die as its accompanying CPU processors.Integrating EDRAM with logic circuits on one single die helps to achievefaster read and write speeds, lower power and smaller form factors.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1A illustrates a perspective view of a meander line resistorstructure is illustrated in accordance with an embodiment;

FIG. 1B illustrates an adjustable meander line resistor in accordancewith an embodiment;

FIG. 1C illustrates a schematic diagram of a control circuit of anadjustable meander line resistor in accordance with an embodiment;

FIG. 1D illustrates an embodiment control circuit of an adjustablemeander line resistor in accordance with an embodiment;

FIG. 2 illustrates a cross sectional view of an adjustable meander lineresistor structure in accordance with an embodiment; and

FIG. 3 illustrates a cross sectional view of an adjustable meander lineresistor structure and an embedded dynamic random access memory cell inaccordance with an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the embodimentsof the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, an adjustable meander line resistor in an embeddeddynamic random access memory (EDRAM) device. The embodiments of thedisclosure may also be applied, however, to a variety of semiconductordevices.

Referring initially to FIG. 1A, a perspective view of a meander lineresistor structure is illustrated in accordance with an embodiment. Themeander line resistor structure 100 may comprise a plurality ofresistors connected in series. As shown in FIG. 1A, the meander lineresistor structure 100 may comprise a first resistor 192, a secondresistor 194, a third resistor 196 and a fourth resistor 198. Themeander line resistor structure 100 may further comprise a plurality ofconnectors, namely a first connector 164, a second connector 166 and athird connector 168. The connectors shown in FIG. 1A may be dopedregions of a semiconductor device. Alternatively, the connectors shownin FIG. 1A may be poly connectors or active layer (OD) connectors.

As shown in FIG. 1A, the first connector 164 is used to connect thefirst resistor 192 and the second resistor 194. Likewise, the secondconnector 166 and the third connector 168 are employed to connect otherresistors so as to form a meander line resistor structure. It should berecognized that while FIG. 1A illustrates the meander line resistorstructure 100 with four resistors connected in series, the meander lineresistor structure 100 could accommodate any number of resistors. Ameander line resistor structure formed by four resistors is illustratedfor simplicity.

Each resistor (e.g., the fourth resistor 198) shown in FIG. 1A may beformed by a plurality of semiconductor vias connected in series. Inaccordance with an embodiment, each resistor (e.g., the fourth resistor198) may be formed by three vias 152, 154 and 156. It should further benoted while FIG. 1A illustrates three vias connected in series, eachresistor may accommodate any number of vias connected in series.Furthermore, the connection of vias illustrated herein is limited solelyfor the purpose of clearly illustrating the inventive aspects of thevarious embodiments. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. For example, thefourth resistor 198 may comprise a plurality of sub-resistors connectedin parallel and each sub-resistor may comprise a plurality of viasconnected in series.

In accordance with an embodiment, the length of the resistors (e.g.,fourth resistor 198) is in a range from 200 nm to 1 um. In accordancewith an embodiment, when the length of the resistor formed by three vias(e.g., fourth resistor 198) is about 740 nm, the total resistance ofthese three vias is about 871.99 ohms. As shown in FIG. 1A, the meanderline resistor structure 100 is formed by four resistors connected inseries. As a result, the total resistance of the meander line resistorstructure 100 is approximately equal to four times 871.99 ohms. Inaddition, one skilled in the art will recognize that the connectors(e.g., first connector 164) may introduce additional resistance, whichis minimal in consideration of the resistance of the resistors (e.g.,the fourth resistor 198).

The meander line resistor structure 100 may be formed on top of activeregions of a semiconductor device. The detailed formation of the meanderline resistor structure 100 will be described below with respect to FIG.2 and FIG. 3. One advantageous feature of having a meander line resistorstructure is that the meander line resistor structure shown in FIG. 1Ahelps to reduce the form factor of a semiconductor resistor so as toachieve a compact semiconductor resistor.

In accordance with an embodiment, the distance between two adjacentresistors (e.g., the first resistor 192 and the second resistor 194) isin a range from 0.03 um to 5 um. It should be noted that the distancedescribed above is merely an example. It may vary depending on differentprocesses. For example, in a 65 nm process, the distance may be in arange from 0.1 um to 1 um. Another advantageous feature of having ameander line resistor structure on top of active regions (not shown butillustrated in FIG. 2 and FIG. 3) of a semiconductor device is that someparasitic parameters such as substrate capacitance may be reducedbecause the meander line resistor structure is not embedded in thesubstrate. In accordance with an embodiment, when the distance betweentwo adjacent resistors is approximately equal to 0.054 um, the parasiticcapacitance of two adjacent resistors is about 0.0125 pF. It should benoted that the parasitic capacitance 0.01256 pF is merely an example.The parasitic capacitance between two adjacent resistors may varydepending on different applications and processes. In sum, the meanderline resistor structure shown in FIG. 1A may help to reduce theparasitic inductance of a semiconductor resistor.

FIG. 1B illustrates an adjustable meander line resistor in accordancewith an embodiment. The adjustable meander line resistor 150 maycomprise a plurality of resistors connected in series. As shown in FIG.1B, the adjustable meander line resistor 150 may comprise a firstresistor 102, a second resistor 104, a third resistor 106, a fourthresistor 108, a fifth resistor 110, a sixth resistor 112, a seventhresistor 114, an eighth resistor 116, a ninth resistor 118 and a tenthresistor 120. The adjustable meander line resistor 150 may furthercomprise a plurality of connectors, namely a first connector 140, asecond connector 142 and a third connector 144.

As shown in FIG. 1B, the first connector 140 is used to connect thesecond resistor 104 and the third resistor 106. Likewise, the secondconnector 142 and the third connector 144 are employed to connect otherresistors so as to form a meander line resistor structure. It should berecognized that while FIG. 1B illustrates the adjustable meander lineresistor 150 with ten resistors connected in series, the adjustablemeander line resistor 150 could accommodate any number of resistors. Anadjustable meander line resistor formed by ten resistors is illustratedfor simplicity.

In order to adjust the resistance of the meander line resistor structureshown in FIG. 1B, the adjustable meander line resistor 150 may furthercomprise a plurality of switches, namely first switch 126, second switch128 and third switch 136. Each switch (e.g., first switch 126) isconnected in parallel with two adjacent resistors. For example, thesecond resistor 104 and the third resistor 106 are connected in seriesusing the first connector 140. The first switch 126 is connected inparallel with the series connected resistors 104 and 106. Furthermore,by turning on the first switch 126, the second resistor 104 and thethird resistor 106 may be bypassed. As a result, the first resistor 102is connected to the fourth resistor 108 through the turned on switch126. Similarly, by turning other switches shown in FIG. 1 (e.g.,switches 128 and 136), the other resistors can be selected to beincluded or excluded from the adjustable meander line resistor 150.

Each resistor (e.g., the tenth resistor 120) shown in FIG. 1B may beformed by a plurality of semiconductor vias connected in series. Inaccordance with an embodiment, each resistor (e.g., the tenth resistor120) may be formed by three vias 152, 154 and 156. The physicalcharacteristics of the vias (e.g., via 152) have been described abovewith respect to FIG. 1A, and hence are not discussed in further detailherein to avoid repetition.

The adjustable meander line resistor 150 may be formed on top of activeregions of a semiconductor device. For example, the second resistor 104and the third resistor 106 are formed on a first doped region 122 and asecond doped region 124 respectively. Furthermore, the first dopedregion 122, the second doped region 124 and a gate stack may form theswitch 126. As such, the second resistor 104 and the third resistor 106are connected to the switch 126. The detailed formation of theadjustable meander line resistor 150 will be described below withrespect to FIG. 2 and FIG. 3. One advantageous feature of having anadjustable meander line resistor is that the meander line resistorstructure shown in FIG. 1B helps to reduce the form factor of asemiconductor resistor so as to achieve a compact semiconductorresistor. In addition, by employing an on and off control of theswitches, different resistance values can be obtained in considerationof different applications.

FIG. 1C illustrates a schematic diagram of a control circuit of anadjustable meander line resistor in accordance with an embodiment. Asshown in FIG. 1C, there may be an adjustable resistor controller 182coupled to the adjustable meander line resistor. In particular, theadjustable resistor controller 182 may generate three gate drive signals184, 186 and 188 for switch 126, switch 128 and switch 136 respectively.By enabling different switches, the total resistance of the meander lineresistor may vary accordingly. For example, by turning on the thirdswitch 136, the resistors 112 and 114 will be bypassed. One skilled inthe art will recognize that there may be eight different combinations bymanipulating three switches. As such, an adjustable resistor havingeight steps may be achieved. Furthermore, it should be noted that thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, the adjustablemeander line resistor could accommodate any number of resistors andswitches.

FIG. 1D illustrates an embodiment control circuit of an adjustablemeander line resistor in accordance with an embodiment. The adjustableresistor controller 182 comprises a bias voltage source 162 and aplurality of resistors connected in series. In accordance with anembodiment, the resistor of the adjustable resistor controller (e.g.,resistor 172) may be a poly resistor. The poly resistors 172, 174 and176 form a voltage divider between the bias voltage source 162 andground. Furthermore, the voltage at each level of the voltage divider(e.g., a joint point between resistor 172 and resistor 174) is furthercoupled to a gate of a corresponding switch. As such, the switch (e.g.,switch 136) can be turned on or off by adjusting the bias voltage source162.

In order to better illustrate the operation of the adjustable resistorcontroller 182 shown in FIG. 1D, an example is illustrated in a table180. As shown in the table 180, the first resistor 172, the secondresistor 174 and the third resistor 176 are defined to be R, 1.5R and 2Rrespectively. One skilled in the art will recognize that the resistanceof a poly resistor can be adjusted by changing either the width orlength of the poly resistor. The values of resistors 172, 174 and 176shown in FIG. 1D are merely an example. Other resistance values may beapplicable in consideration with different applications. Furthermore,while FIG. 1D shows the divider is formed by a plurality of resistors(e.g., resistor 172), the divider can be formed by other passivecomponents. For example, the divider can be formed by a plurality ofcapacitors. In accordance with an embodiment, the capacitors can bemetal oxide silicon varactor (MOSVAR), metal insulator metal (MIM)capacitor, metal oxide metal (MOM) capacitor or the like.

FIG. 1D further illustrates an adjustable meander line resistor may beobtained by adjusting a bias voltage source. As shown in the table 180,by applying different bias voltages, the voltage across each resistor(e.g., resistor 176) varies accordingly. For example, when the biasvoltage is set to be zero, the voltage across each resistor is equal tozero. As a result, all resistors (e.g., 104, 106, 108, 110, 112 and 114)are included into the meander line resistor. On the other hand, when thebias voltage is increase to 0.7V, the voltage at the gate of the switch126 is up to 0.7V, which is high enough to turn on the switch 126. As aresult, the resistor 104 and the resistor 106 are bypassed and notincluded in the adjustable meander line resistor. Similarly, by furtherincreasing the bias voltage, additional switches may be turned onaccordingly. As such, an adjustable meander line resistor may beobtained by controlling the bias voltage source 162.

FIG. 2 illustrates a cross sectional view of an adjustable meander lineresistor structure in accordance with an embodiment. As shown in FIG. 2,the semiconductor device 200 may comprise a plurality of semiconductorlayers. A substrate 210 may comprise bulk silicon, doped or undoped, oran active layer of a silicon-on-insulator (SOI) substrate. Generally, anSOI substrate comprises a layer of a semiconductor material such assilicon, germanium, silicon germanium, SOT, silicon germanium oninsulator (SGOI), or combinations thereof. Other substrates that may beused include multi-layered substrates, gradient substrates, or hybridorientation substrates.

The substrate 210 may comprise a variety of electrical circuits (notshown). The electrical circuits formed on the substrate 210 may be anytype of circuitry suitable for a particular application. In accordancewith an embodiment, the electrical circuits may include various n-typemetal-oxide semiconductor (NMOS) and/or p-type metal-oxide semiconductor(PMOS) devices such as transistors, capacitors, resistors, diodes,photo-diodes, fuses and the like. The electrical circuits may beinterconnected to perform one or more functions. The functions mayinclude memory structures, processing structures, sensors, amplifiers,power distribution, input/output circuitry or the like. One of ordinaryskill in the art will appreciate that the above examples are providedfor illustrative purposes only to further explain applications of thepresent disclosure and are not meant to limit the present disclosure inany manner.

As shown in FIG. 2, the substrate 210 may comprise a plurality of dopedregions, namely a first doped region 212, a second doped region 214, athird doped region 216, a fourth doped region 218 and a fifth dopedregion 219. Doped regions (e.g., first doped region 212) may be formedin the substrate 210 on opposing sides of a gate stack 202. In anembodiment in which the substrate 210 is an n-type substrate, the dopedregions (e.g., first doped region 212) may be formed by implantingappropriate p-type dopants such as boron, gallium, indium or the like.Alternatively, in an embodiment in which the substrate 210 is a p-typesubstrate, the doped regions (e.g., first doped region 212) may beformed by implanting appropriate n-type dopants such as phosphorous,arsenic or the like. It should be noted that the first doped region 212,the second doped region 214 and the gate stack 202 may form a firstswitch. Similarly, the second doped region, the third doped region 216and the gate stack 204 may form a second switch.

The first interlayer dielectric (ILD) layer 220 may be formed over thesubstrate 210. The first ILD layer 220 may be formed by chemical vapordeposition, sputtering, or any other methods known and used in the artfor forming an ILD. The first ILD layer 220 may comprise doped orundoped silicon oxide, although other materials such as silicon nitridedoped silicate glass, high-k materials, combinations of these, or thelike, may alternatively be utilized. After formation, the first ILDlayer 220 may be planarized using suitable techniques such as a chemicalmechanical polish (CMP) process.

The second ILD layer 230 may be formed over the first ILD layer 220 andthe third ILD layer 240 may be formed over the second ILD layer 230. Thefabrication processes of the second ILD layer 230 and the third ILDlayer 240 are similar to that of the first ILD layer 220, and hence arenot described in further detail herein. As shown in FIG. 2, there may bea plurality of vias formed in each ILD layer. In particular, in thefirst ILD layer 220, a via 222 is formed over a first active region 212.Vias 224 and 226 are formed over a second active region 214. A via 228is formed over a third active region 216. Similarly, vias 223, 225 and227 are formed over the fourth and fifth active regions respectively. Inthe second ILD layer 230, vias 232, 234, 236, 238, 233, 235 and 237 areformed over vias 222, 224, 226, 228, 223, 225 and 227 respectively. Inthe third ILD layer 240, vias 242, 244, 246, 248, 243, 245 and 247 areformed over vias 232, 234, 236, 238, 233, 235 and 237 respectively. As aresult, vias 222, 232 and 242 form a first resistor. Likewise, othervias form other resistors.

Furthermore, by using an interconnector (e.g., first interconnector 252of a bottom metallization layer 250), two adjacent resistors shown inFIG. 2 are connected in series to form a series resistor circuit.Moreover, a plurality of series resistor circuits are further connectedtogether to form a meander line resistor structure. FIG. 2 furtherillustrates a plurality of switches, each of which is connected inparallel with its corresponding series resistor circuit. For example,the first doped region 212, the first gate 202 and the second dopedregion 214 form a first switch, which is connected in parallel with thefirst series resistor circuit (vias 222, 232, 242, connector 252, vias244, 234 and 224). By controlling the on and off of the first switch,the first series resistor circuit will be included in or exclude fromthe adjustable meander line resistor.

The bottom metallization layer 250 is formed over the third ILD layer240. As shown in FIG. 2, the bottom metallization layer 250 comprises aplurality of interconnectors (e.g., first connector 252). Theinterconnectors (e.g., first interconnector 252) are formed of metalmaterials such as copper or copper alloys and the like. Likewise, thetop metallization layer 260 comprises a plurality of interconnectors(not shown). The metallization layers 250 and 260 may be formed throughany suitable techniques such as deposition, damascene and the like.

It should be noted while FIG. 2 shows the bottom metallization layer 250and the top metallization layer 260, one skilled in the art willrecognize that one or more inter-metal dielectric layers (not shown) andthe associated metallization layers (not shown) are formed between thebottom metallization layer 250 and the top metallization layer 260. Inparticular, the layers between the bottom metallization layer 250 andthe top metallization layer 260 may be formed by alternating layers ofdielectric (e.g., extremely low-k dielectric material) and conductivematerials (e.g., copper).

FIG. 3 illustrates a cross sectional view of a meander line resistorstructure and an EDRAM cell in accordance with an embodiment. A meanderline resistor structure 362 may be fabricated in the same semiconductordie as an embedded DRAM cell 364. The semiconductor die 300 may comprisea substrate 210, a first ILD 220, a second ILD 230, a third ILD layer240 and a first metallization layer 250. The fabrication process of eachlayer (e.g., first ILD 220) has been described above with respect toFIG. 2, and hence is not discussed herein to avoid unnecessaryrepetition.

As shown in FIG. 3, the substrate 210 may comprise a plurality ofisolation regions (e.g., first isolation region 218) and a plurality ofactive regions (e.g., first active region 316). The first active region316 and the second region 318 form the source and drain regions of thefirst MOS transistor 302. The third active region 312 and the fourthactive region 314 form the source and drain regions of the second MOStransistor 304. The first MOS transistor 302 and the second MOStransistor 304 are separated by a second isolation region 228.

The isolation regions (e.g., second isolation region 228) may be shallowtrench isolation (STI) regions, and may be formed by etching thesubstrate 210 to form a trench and filling the trench with a dielectricmaterial. In accordance with an embodiment, the isolation regions may befilled with a dielectric material such as an oxide material, ahigh-density plasma (HDP) oxide or the like.

The first MOS transistor 302 and the second MOS transistor 304 furthercomprise gate stacks formed in the first ILD layer 220. The gate stacksmay comprise gate dielectrics 308, gate electrodes 306, and spacers 303.The gate dielectrics 308 may be a dielectric material such as siliconoxide, silicon oxynitride, silicon nitride, an oxide, anitrogen-containing oxide, a combination thereof, or the like. Inaccordance with an embodiment, the gate dielectrics 308 may comprise anoxide layer formed by suitable oxidation processes such as a wet or drythermal oxidation in an ambient comprising an oxide, H₂O, NO, or acombination thereof.

The gate electrodes 306 may comprise conductive materials such as metals(e.g., tantalum, titanium, molybdenum, tungsten, platinum, aluminum,hafnium, ruthenium and the like), metal silicide materials (e.g.,titanium silicide, cobalt silicide, nickel silicide, tantalum silicideand the like), metal nitride materials (e.g., titanium nitride, tantalumnitride and the like), doped poly-crystalline silicon, other conductivematerials, combinations thereof. In accordance with an embodiment, thegate electrodes 306 may be poly-silicon formed by depositing doped orundoped poly-silicon by low-pressure chemical vapor deposition (LPCVD).The spacers 303 may be formed by blanket depositing one or more spacerlayers (not shown) over the gate electrodes 306 and the substrate 210.The spacer layers may comprise SiN, oxynitride, SiC, SiON, oxide, andthe like and may be formed by commonly used methods such CVD, plasmaenhanced CVD, sputter, and other suitable techniques.

The meander line resistor structure 362 is formed by a plurality ofresistors (e.g., resistors 372 and 374), each of which is formed on anactive region of substrate 210. In particular, a first resistor 372 isformed on a first doped region 316 and a second resistor 374 is formedon a second doped region 318. As shown in FIG. 3, each resistor maycomprise three vias connected in series. For example, the first resistor372 comprises the first via 326, the second via 336 and the third via346. The first via 326, the second via 336 and the third via 346 arelocated in the first ILD layer 220, the second ILD layer 230 and thethird ILD layer 240 respectively. The interconnector 354 connects thefirst resistor 372 and the second resistor 374 in series.

For simplicity, the meander line resistor structure 362 comprises tworesistors connected in series. However, a person skilled in the art willrecognize that the meander line resistor structure 362 may accommodateany number of resistors connected in series. In addition, while FIG. 3illustrates a single via in each ILD layer (e.g., second via 336 in thesecond ILD layer 230), this diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.For example, the second via 336 may be replaced by a plurality of secondILD layer vias connected in parallel.

The EDRAM cell 364 may comprise the second MOS transistor 304 and acapacitor formed by a first capacitor plate 334, a capacitor dielectriclayer 342 and a second capacitor plate 344. As shown in FIG. 3, afterthe first ILD layer 220 layer has been formed, a capacitor contact 322and a lower bit line contact 324 may be formed through the first ILDlayer 220. In an embodiment the capacitor contact 322 may be formed toprovide an electrical connection between the fourth active region 314and the first capacitor plate 334. The lower bit line contact 324 may beformed to provide an electrical connection between the third activeregion 312 and an upper bit line contact 348.

The capacitor contact 322 and the lower bit line contact 324 may beformed by suitable techniques such as a damascene process. It should benoted that the capacitor contact 322 and the lower bit line contact 324may comprise one or more layers of conductive material. For example, thecapacitor contact 322 and the lower bit line contact 324 may includebarrier layers, adhesive layers, multiple conductive layers or the like.

The first etch stop layer 332 may be formed over the first ILD layer 220in order to provide a control point for a subsequent etch process. Thefirst etch stop layer 332 may be a dielectric material such as SiN, SiONor the like. In accordance with an embodiment the first etch stop layer322 may be formed using any suitable processes such as CVD, PECVD, ALDor the like.

Once the second ILD layer 230 has been formed, the second ILD layer 230and the first etch stop layer 332 may be patterned in order to exposethe underlying capacitor contact 322 and to provide an opening in thesecond ILD layer 230 in which the first capacitor plate 334 may beformed. The second ILD layer 230 and the first etch stop layer 332 maybe patterned using suitable photolithographic masking and etchingprocesses. Once the second ILD layer 230 and the first etch stop layer332 have been patterned, the first capacitor plate 334 may be formed inelectrical contact with the capacitor contact 322. The first capacitorplate 334 may be formed by depositing and patterning a layer ofconductive material such as TiN, TaN, ruthenium or the like. The firstcapacitor plate 224 may be formed by suitable techniques such as CVD,ALD or the like. The capacitor dielectric layer 342 is formed over thefirst capacitor plate 334. The capacitor dielectric layer 342 is formedof capacitive dielectric materials such as silicon oxide capacitivedielectric materials, silicon nitride capacitive dielectric materials,silicon oxynitride capacitive dielectric materials and/or the like. Thesecond capacitor plate 344 may be formed of a conductive material suchas TiN, TaN, ruthenium, aluminum, tungsten, copper, combinations ofthese or the like. The second capacitor plate 344 may be formed by usinga suitable process such as CVD, PECVD, ALD or the like.

After the third ILD layer 240 has been formed, the upper bit linecontact 348 may be formed to extend through the third ILD layer 240 andthe second ILD layer 230. The upper bit line contact 348 may be formedusing any suitable techniques such as a damascene process. It should benoted that the upper bit line contact 348 may comprise one or morelayers of conductive material. For example, the upper bit line contact348 may include barrier layers, adhesive layers, multiple conductivelayers or the like. The bit line 352 may be electrically coupled withthe third active region 312 in the substrate 210 through the lower bitline contact 324 and the upper bit line contact 348. The bit line 352may be formed by suitable techniques such as a damascene process.

Although embodiments of the present disclosure and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. An apparatus comprising: a substrate comprising aplurality of active regions; a plurality of gate stacks disposed overthe substrate wherein each gate stack is formed between two adjacentactive regions; a first resistor having a first bottom terminal disposedover and in direct contact with a first active region of the pluralityof active regions and a first upper terminal coupled to a firstconnector, wherein the first resistor is formed by a plurality of firstvias connected in series, and wherein two adjacent first vias are indirect contact to each other, and wherein a bottom via of the firstresistor and the gate stacks are formed in an interlayer dielectriclayer; a second resistor having a second bottom terminal disposed overand in direct contact with a second active region of the plurality ofactive regions and a second upper terminal coupled to the firstconnector; a switch formed by the first active region, the second activeregion and a first gate of the plurality of gate stacks, wherein thefirst active region, the first resistor, the first connector, the secondresistor and the second active region form a U-shaped structure and thefirst gate is surrounded by the U-shaped structure; and a third resistorhaving a third bottom terminal disposed over and in direct contact withthe second active region, wherein the third bottom terminal of the thirdresistor is coupled to the second bottom terminal of the secondresistor.
 2. The apparatus of claim 1, wherein: the second resistor isformed by a plurality of second vias connected in series; and the thirdresistor is formed by a plurality of third vias connected in series. 3.The apparatus of claim 2, further comprising: a first interlayerdielectric layer formed over the substrate, wherein one of the firstvias, one of the second vias and one of the third vias are embedded inthe first interlayer dielectric layer; a second interlayer dielectriclayer formed over the first interlayer dielectric layer, wherein one ofthe first vias, one of the second vias and one of the third vias areembedded in the second interlayer dielectric layer; and a thirdinterlayer dielectric layer formed over the second interlayer dielectriclayer, wherein one of the first vias, one of the second vias and one ofthe third vias are embedded in the third interlayer dielectric layer. 4.The apparatus of claim 3, further comprising: a first metallizationlayer formed over the third interlayer dielectric layer, wherein thefirst connector is embedded in the first metallization layer.
 5. Theapparatus of claim 1, wherein the first resistor, the second resistorand the third resistor form an adjustable meander line resistor.
 6. Theapparatus of claim 5, further comprising: an adjustable resistorcontroller configured to generate a gate drive signal coupled to thefirst gate of the switch.
 7. The apparatus of claim 5, furthercomprising: a bias voltage source coupled to a voltage divider, whereina voltage output of the voltage divider is coupled to the gate of theswitch wherein the bias voltage source is configured such that: thefirst resistor and the second resistor are bypassed from the meanderline resistor when a gate voltage of the switch is more than a thresholdvoltage of the switch; and the first resistor and the second resistorare included into the meander line resistor when the gate voltage of theswitch is less than the threshold voltage of the switch.
 8. A systemcomprising: a first interlayer dielectric layer formed over a substrate,wherein the first interlayer dielectric layer comprises a first gatestack and a second gate stack; a second interlayer dielectric layerformed over the first interlayer dielectric layer; a third interlayerdielectric layer formed over the second interlayer dielectric layer; anadjustable meander line resistor comprising: a first resistor formedover a first active region of the substrate; a second resistor formedover a second active region of the substrate; a third resistor formedover the second active region of the substrate; and a first seriescircuit formed by the first resistor, the second resistor and aconnector connected in series; a first switch connected in parallel withthe first series circuit, wherein the first switch comprises: the firstgate; the first active region; and the second active region; and adynamic random access memory (DRAM) cell formed adjacent to theadjustable meander line resistor comprising: a DRAM transistor formed inthe substrate, wherein the DRAM transistor comprises the second gatestack; a first conductive capacitor plate formed in the secondinterlayer dielectric layer; a second conductive capacitor plate formedin the third interlayer dielectric layer; and a capacitor dielectriclayer formed between the first conductive capacitor plate and the secondconductive capacitor plate.
 9. The system of claim 8, furthercomprising: a bit line formed over the third interlayer dielectriclayer; a first bit line contact formed in the first interlayerdielectric layer, wherein the first bit line contact is coupled to afirst doped region of the DRAM transistor; a second bit line contactformed between the bit line and the first bit line contact; and acapacitor contact coupled to the first conductive capacitor plate,wherein the capacitor contact is coupled to a second doped region of theDRAM transistor.
 10. The system of claim 8, wherein the first resistorcomprises a first via, a second via and a third via connected in series,wherein: the first via is formed by a plurality of first interlayer viasconnected in parallel; the second via is formed by a plurality of secondinterlayer vias connected in parallel; and the third via is formed by aplurality of third interlayer vias connected in parallel.
 11. The systemof claim 10, wherein: the first interlayer via is embedded in the firstinterlayer dielectric layer; the second interlayer via is embedded inthe second interlayer dielectric layer; and the third interlayer via isembedded in the third interlayer dielectric layer.
 12. The system ofclaim 8, further comprising: a second series circuit connected to thefirst series circuit in series, wherein a second switch is connected tothe second series circuit in parallel; and a third series circuitconnected to the second series circuit in series, wherein a third switchis connected to the third series circuit in parallel.
 13. The system ofclaim 12, further comprising a control circuit comprising: a biasvoltage source; and a voltage divider coupled to the bias voltagesource, the first switch, the second switch and the third switch. 14.The system of claim 13, wherein the bias voltage source is configuredsuch that: a first series circuit is included into the adjustablemeander line resistor when a gate voltage from the voltage divider isless than a threshold voltage of the first switch; and a first seriescircuit is excluded from the adjustable meander line resistor when thegate voltage from the voltage divider is greater than the thresholdvoltage of the first switch.
 15. A method comprising: providing asubstrate with a first conductivity type; forming a first transistorcomprising: forming a first doped region with a second conductivitytype; forming a second doped region with the second conductivity type;and forming a first gate; forming a first series circuit connected inparallel with the first transistor comprising: forming a first resistorover the first doped region, wherein the first resistor is formed by aplurality of first vias connected in series, and wherein two adjacentfirst vias are in direct contact to each other, and wherein a bottom viaof the first resistor and the first gate are formed in an interlayerdielectric layer; forming a second resistor over the second dopedregion; and coupling the first resistor and the second resistor with afirst connector, wherein the first doped region, the first resistor, thefirst connector, the second resistor and the second doped region form aU-shaped structure and the first gate is surrounded by the U-shapedstructure; and configuring a first control circuit to generate a firstgate signal of the first transistor.
 16. The method of claim 15, furthercomprising: forming a second transistor connected in series with thefirst transistor comprising the second doped region, a third dopedregion and a second gate; forming a second series circuit connected inparallel with the second transistor comprising: forming a third resistorover the second doped region; forming a fourth resistor over the thirddoped region; and coupling the third resistor and the fourth resistorwith a second connector; and configuring a second control circuit togenerate a second gate signal of the second transistor.
 17. The methodof claim 16, further comprising: depositing a first interlayerdielectric layer comprising the first gate and the second gate;embedding a first interlayer via in the first interlayer dielectriclayer; depositing a second interlayer dielectric layer over the firstinterlayer dielectric layer; embedding a second interlayer via in thesecond interlayer dielectric layer; depositing a third interlayerdielectric layer over the second interlayer dielectric layer; andembedding a third interlayer via in the third interlayer dielectriclayer.
 18. The method of claim 17, further comprising: aligning thefirst interlayer via, the second interlayer via and the third interlayervia to form the first resistor.
 19. The method of claim 15, furthercomprising: forming a voltage divider using a plurality of polyresistors; and coupling a bias voltage source with the voltage divider.20. The method of claim 19, further comprising: configuring the biasvoltage source to generate a gate signal for controlling the first gateof the first transistor.